Abstract 2548: The central nervous system immune cell interactome is a function of cancer lineage, tumor microenvironment and STAT3 expression

Introduction: Deconstructive immune cell profiling of central nervous system (CNS) tumors has focused on the tumor, excluding interrogation of the tumor microenvironment (TME). Integrated spatial analysis can ascertain the cell interactome and may be a key biomarker for effective anti-tumor immune responses.

Methods: En bloc resections of glioma (n=10) and lung metastasis (n=10) to preserve the tissue architecture, underwent tissue segmentation and high dimension opal 7-color multiplex imaging. Bioinformatic analysis of scRNA was used to infer immune cell functionality.

Results: CD3+ T cell frequency was equivalent between CNS cancer lineages. Within gliomas T cells were confined to the perivascular space and the infiltrating edge. In lung metastasis, T cells are confined to the tumor stroma. CD163+ macrophages predominate in brain metastasis throughout the TME (p<0.05), while CD68+ monocytes (CD68+, CD11c+CD68+, and CD11+CD68+CD163+) are more common in gliomas (p<0.05). T cell dyad and cluster immune interactions were more common in the absence of nuclear STAT3 expression. T cells usually interact with CD163+ macrophages as dyads in metastasis at the brain interface (p=0.031) and within tumor (p=0.0009); in clusters throughout the TME (interface: p=0.024; tumor: p=0.01; necrosis: p=0.045), and as STAT3+ dyads and cluster interactions in the tumor (p<0.05). Immune suppressed CD11c+CD163+ dendritic cells (tumor: p=0.036; and necrosis p=0.020) predominate in metastasis. In contrast, gliomas typically lacked dyad and cluster interactions except for T cell and CD68+ dyads in the tumor (p=0.023). Bioinformatic analysis of CD45+ scRNA seq data revealed that the majority of innate immune populations express both pro-inflammatory and immune suppressive genes and that subsets of CD68+ and CD11c+CD68+ cells expressed markers such as TMEM119, P2YR13 and CX3CR1 that identify microglia.

Conclusion: Current therapies are targeted to cell populations and singular pathways. Immunosuppressive macrophages dominate within the TME and targeting this population may create an environment that favors T cell activation and effective immune responses. Furthermore, the immune interactome, an important event for anti-tumor immune response, is a function of cancer lineage, TME, and STAT3 expression, which will gain relevance for future therapeutics directed to modulating these interactions.

Citation Format: Hinda Najem, Martina Ott, Cynthia Kassab, Arvind Rao, Ganesh Rao, Anantha Marisetty, Adam M. Sonabend, Craig Horbinski, Roel Verhaak, Anand Shakar, Santhoshi Krishnan, Frederick S. Varn, Victor A. Arietta, Pravesh Gupta, Sherise D. Ferguson, Jason Huse, Gregory N. Fuller, James Long, Dan Winskowski, Ben Freiberg, C. David James, Leonidas C. Platanias, Maciej S. Lesniak, Jared K. Burks, Amy B. Heimberger. The central nervous system immune cell interactome is a function of cancer lineage, tumor microenvironment and STAT3 expression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2548.

B7-H3 Specific CAR T Cells for the Naturally Occurring, Spontaneous Canine Sarcoma Model

One obstacle for human solid tumor immunotherapy research is the lack of clinically relevant animal models. In this study, we sought to establish a chimeric antigen receptor (CAR) T-cell treatment model for naturally occurring canine sarcomas as a model for human CAR T-cell therapy. Canine CARs specific for B7-H3 were constructed using a single-chain variable fragment derived from the human B7-H3-specific antibody MGA271, which we confirmed to be cross-reactive with canine B7-H3. After refining activation, transduction, and expansion methods, we confirmed target killing in a tumor spheroid three-dimensional assay. We designed a B7-H3 canine CAR T-cell and achieved consistently high levels of transduction efficacy, expansion, and in vitro tumor killing. Safety of the CAR T cells were confirmed in two purposely bred healthy canine subjects following lymphodepletion by cyclophosphamide and fludarabine. Immune response, clinical parameters, and manifestation were closely monitored after treatments and were shown to resemble that of humans. No severe adverse events were observed. In summary, we demonstrated that similar to human cancers, B7-H3 can serve as a target for canine solid tumors. We successfully generated highly functional canine B7-H3-specific CAR T-cell products using a production protocol that closely models human CAR T-cell production procedure. The treatment regimen that we designed was confirmed to be safe in vivo. Our research provides a promising direction to establish in vitro and in vivo models for immunotherapy for canine and human solid tumor treatment.

A first-in-human Phase I trial of the oral p-STAT3 inhibitor WP1066 in patients with recurrent malignant glioma

Aim: To ascertain the maximum tolerated dose (MTD)/maximum feasible dose (MFD) of WP1066 and p-STAT3 target engagement within recurrent glioblastoma (GBM) patients. Patients & methods: In a first-in-human open-label, single-center, single-arm 3 + 3 design Phase I clinical trial, eight patients were treated with WP1066 until disease progression or unacceptable toxicities. Results: In the absence of significant toxicity, the MFD was identified to be 8 mg/kg. The most common adverse event was grade 1 nausea and diarrhea in 50% of patients. No treatment-related deaths occurred; 6 of 8 patients died from disease progression and one was lost to follow-up. Of 8 patients with radiographic follow-up, all had progressive disease. The longest response duration exceeded 3.25 months. The median progression-free survival (PFS) time was 2.3 months (95% CI: 1.7 months-NA months), and 6-month PFS (PFS6) rate was 0%. The median overall survival (OS) rate was 25 months (95% CI: 22.5 months-NA months), with an estimated 1-year OS rate of 100%. Pharmacokinetic (PK) data demonstrated that at 8 mg/kg, the T1/2 was 2-3 h with a dose dependent increase in the Cmax. Immune monitoring of the peripheral blood demonstrated that there was p-STAT3 suppression starting at a dose of 1 mg/kg. Conclusion: Immune analyses indicated that WP1066 inhibited systemic immune p-STAT3. WP1066 had an MFD identified at 8 mg/kg which is the target allometric dose based on prior preclinical modeling in combination with radiation therapy and a Phase II study is being planned for newly diagnosed MGMT promoter unmethylated glioblastoma patients.

A phase I/IIa, open-label, multicenter, non-randomized clinical trial to assess the safety and efficacy of CYNK-001 in combination with recombinant human interleukin 2 in adults with recurrent resection eligible IDH1 wild-type glioblastoma (GBM)

TPS2080

Background: CYNK-001 is a CD56+CD3- enriched, off-the-shelf, allogeneic natural killer (NK) cell product expanded from placental CD34 cells. CYNK-001 exhibits in vitro cytotoxicity against patient-derived GBM cell lines and secretes cytolytic cytokines during co-culture with cancer cells. CYNK-001 administered via the intracranial (IC) route exhibited in vivo antitumor activity in a U-87MG orthotopic mouse model. Methods: A Phase I/IIa clinical trial is enrolling IDH1 wild-type GBM patients at first or second recurrence with contrast-enhancing measurable disease (per RANO criteria) who are candidate for surgical resection. Screening MRI scans for inclusion are performed within 14 days prior to Day -5 lymphodepletion with Cyclophosphamide 900mg/m2 and fludarabine 30mg/m2 plus mesna. Using a standard 3+3 dose escalation schema, patients will receive the first cycle of CYNK-001 intravenously (IV) at an initial dose of 2.4 x109 cells on Days 1, 8 and 15 after lymphodepletion. Cell supportive IL-2 at 6M IU administered SQ on Days 1, 3, 5, 8, 10, 12, and 15 within 3 hours prior to CYNK-001 IV infusion where applicable. Cycle 2 begins with surgical resection on Day 22 in which CYNK-001 is administered directly into the tumor cavity wall at an initial dose of 100 x106 NK cells and an Ommaya catheter placement. Subsequent CYNK-001 IC administrations via the Ommaya are on days 29 and 36 with 6M IU IL-2 SQ. DLT is evaluated for all dosing cohorts from day 1 to 7 days post last dose of cycle 2. Once a maximum tolerated dose is identified, a safety lead-in cohort with an additional 3 cycles of CYNK-001 IC will be administered prior to initiating the Phase IIa portion of the study. Endpoints: The primary endpoint is dose-limiting toxicity for the Phase I analysis and 6-month progression free survival post tumor resection for the Phase IIa component. Post-resected tumor tissue will be characterized for effector immune cell function and immune suppression with assessments directed at CYNK-001 tumor distribution using methodology developed at Celularity Inc. Approximately 66 patients are planned for this Phase I/IIa study. Approximately 66 patients are planned for this Phase I/IIa study. Clinical trial information: NCT05218408.

A Window of Opportunity to Overcome Therapeutic Failure in Neuro-Oncology

Glioblastoma is the most common primary malignant brain neoplasm and it remains one of the most difficult-to-treat human cancers despite decades of discovery and translational and clinical research. Many advances have been made in our understanding of the genetics and epigenetics of gliomas in general; yet, there remains an urgent need to develop novel agents that will improve the survival of patients with this deadly disease. What sets glioblastoma apart from all other cancers is that it develops and spreads within an organ that renders tumor cells inaccessible to most systemically administered agents because of the presence of the blood-brain barrier. Inadequate drug penetration into the central nervous system is often cited as the most common cause of trial failure in neuro-oncology, and even so-called brain-penetrant therapeutics may not reach biologically relevant concentrations in tumor cells. Evaluation of the pharmacokinetics and pharmacodynamics of a novel therapy is a cornerstone of drug development, but few trials for glioma therapeutics have incorporated these basic elements in an organ-specific manner. Window-of-opportunity clinical trial designs can provide early insight into the biological plausibility of a novel therapeutic strategy in the clinical setting. A variety of window-of-opportunity trial designs, which take into account the limited access to treated tissue and the challenges with obtaining pretreatment control tissues, have been used for the initial development of traditional and targeted small-molecule drugs and biologic therapies, including immunotherapies and oncolytic viral therapies. Early-stage development of glioma therapeutics should include a window-of-opportunity component whenever feasible.

Cell-directed aptamer therapeutic targeting for cancers including those within the central nervous system

Osteopontin (OPN) is produced by tumor cells as well as by myeloid cells and is enriched in the tumor microenvironment (TME) of many cancers. Given the roles of OPN in tumor progression and immune suppression, we hypothesized that targeting OPN with aptamers that have high affinity and specificity could be a promising therapeutic strategy. Bi-specific aptamers targeting ligands for cellular internalization were conjugated to siRNAs to suppress OPN were created, and therapeutic leads were selected based on target engagement and in vivo activity. Aptamers as carriers for siRNA approaches were created including a cancer targeting nucleolin aptamer Ncl-OPN siRNA and a myeloid targeting CpG oligodeoxynucleotide (ODN)-OPN siRNA conjugate. These aptamers were selected as therapeutic leads based on 70–90% OPN inhibition in cancer (GL261, 344SQ, 4T1B2b) and myeloid (DC2.4) cells relative to scramble controls. In established immune competent 344SQ lung cancer and 4T1B2b breast cancer models, these aptamers, including in combination, demonstrate therapeutic activity by inhibiting tumor growth. The Ncl-OPN siRNA aptamer demonstrated efficacy in an immune competent orthotopic glioma model administered systemically secondary to the ability of the aptamer to access the glioma TME. Therapeutic activity was demonstrated using both aptamers in a breast cancer brain metastasis model. Targeted inhibition of OPN in tumor cells and myeloid cells using bifunctional aptamers that are internalized by specific cell types and suppress OPN expression once internalized may have clinical potential in cancer treatment.

Circadian Regulator CLOCK Drives Immunosuppression in Glioblastoma

The symbiotic interactions between cancer stem cells and the tumor microenvironment (TME) are critical for tumor progression. However, the molecular mechanism underlying this symbiosis in glioblastoma (GBM) remains enigmatic. Here, we show that circadian locomotor output cycles kaput (CLOCK) and its heterodimeric partner brain and muscle ARNT-like 1 (BMAL1) in glioma stem cells (GSCs) drive immunosuppression in GBM. Integrated analyses of the data from transcriptome profiling, single-cell RNA sequencing, and TCGA datasets, coupled with functional studies, identified legumain (LGMN) as a direct transcriptional target of the CLOCK-BMAL1 complex in GSCs. Moreover, CLOCK-directed olfactomedin-like 3 (OLFML3) upregulates LGMN in GSCs via hypoxia-inducible factor 1-alpha (HIF1α) signaling. Consequently, LGMN promotes microglial infiltration into the GBM TME via upregulating CD162 and polarizes infiltrating microglia towards an immune-suppressive phenotype. In GBM mouse models, inhibition of the CLOCK-OLFML3-HIF1α-LGMN-CD162 axis reduces intratumoral immune-suppressive microglia, increases CD8+ T-cell infiltration, activation and cytotoxicity, and synergizes with anti-PD1 therapy. In human GBM, the CLOCK-regulated LGMN signaling correlates positively with microglial abundance and poor prognosis. Together, these findings uncover the CLOCK-OLFML3-HIF1α-LGMN axis as a molecular switch that controls microglial biology and immunosuppression, thus revealing potential new therapeutic targets for GBM patients.

Central nervous system immune interactome is function of cancer lineage, tumor microenvironment and STAT3 expression

BACKGROUND

Immune cell profiling of primary and metastatic CNS tumors has been focused on the tumor, not the tumor microenvironment (TME), or has been analyzed via biopsies.

METHODS

En bloc resections of gliomas (n = 10) and lung metastases (n = 10) were analyzed via tissue segmentation and high-dimension Opal 7-color multiplex imaging. Single-cell RNA analyses were used to infer immune cell functionality.

RESULTS

Within gliomas, T cells were localized in the infiltrating edge and perivascular space of tumors, while residing mostly in the stroma of metastatic tumors. CD163⁺ macrophages were evident throughout the TME of metastatic tumors, whereas in gliomas, CD68⁺, CD11c⁺CD68⁺, and CD11c⁺CD68⁺CD163⁺ cell subtypes were commonly observed. In lung metastases, T cells interacted with CD163⁺ macrophages as dyads and clusters at the brain-tumor interface and within the tumor itself and as clusters within the necrotic core. In contrast, gliomas typically lacked dyad and cluster interactions, except for T cell CD68⁺ cell dyads within the tumor. Analysis of transcriptomic data in glioblastomas revealed that innate immune cells expressed both proinflammatory and immunosuppressive gene signatures.

CONCLUSION

Our results show that immunosuppressive macrophages are abundant within the TME and that the immune cell interactome between cancer lineages is distinct. Further, these data provide information for evaluating the role of different immune cell populations in brain tumor growth and therapeutic responses.

FUNDING

This study was supported by the NIH (NS120547), a Developmental research project award (P50CA221747), ReMission Alliance, institutional funding from Northwestern University and the Lurie Comprehensive Cancer Center, and gifts from the Mosky family and Perry McKay. Performed in the Flow Cytometry & Cellular Imaging Core Facility at MD Anderson Cancer Center, this study received support in part from the NIH (CA016672) and the National Cancer Institute (NCI) Research Specialist award 1 (R50 CA243707). Additional support was provided by CCSG Bioinformatics Shared Resource 5 (P30 CA046592), a gift from Agilent Technologies, a Research Scholar Grant from the American Cancer Society (RSG-16-005-01), a Precision Health Investigator Award from University of Michigan (U-M) Precision Health, the NCI (R37-CA214955), startup institutional research funds from U-M, and a Biomedical Informatics & Data Science Training Grant (T32GM141746).

Designing Clinical Trials for Combination Immunotherapy: A Framework for Glioblastoma

Immunotherapy has revolutionized treatment for many hard-to-treat cancers but has yet to produce significant improvement in outcomes for patients with glioblastoma. This reflects the multiple and unique mechanisms of immune evasion and escape in this highly heterogeneous tumor. Glioblastoma engenders profound local and systemic immunosuppression and is remarkably effective at inducing T-cell dysfunction, posing a challenge to any immunotherapy-based approach. To overcome these mechanisms, multiple disparate modes of immune-oriented therapy will be required. However, designing trials that can evaluate these combinatorial approaches requires careful consideration. In this review, we explore the immunotherapy resistance mechanisms that have been encountered to date and how combinatorial approaches may address these. We also describe the unique aspects of trial design in both preclinical and clinical settings and consider endpoints and markers of response best suited for an intervention involving multiple agents.

The Eclectic Nature of Glioma-Infiltrating Macrophages and Microglia

Glioblastomas (GBMs) are complex ecosystems composed of highly multifaceted tumor and myeloid cells capable of responding to different environmental pressures, including therapies. Recent studies have uncovered the diverse phenotypical identities of brain-populating myeloid cells. Differences in the immune proportions and phenotypes within tumors seem to be dictated by molecular features of glioma cells. Furthermore, increasing evidence underscores the significance of interactions between myeloid cells and glioma cells that allow them to evolve in a synergistic fashion to sustain tumor growth. In this review, we revisit the current understanding of glioma-infiltrating myeloid cells and their dialogue with tumor cells in consideration of their increasing recognition in response and resistance to immunotherapies as well as the immune impact of the current chemoradiotherapy used to treat gliomas.

BIOM-31. ERK1/2 PHOSPHORYLATION PREDICTS SURVIVAL FOLLOWING ANTI-PD-1 IMMUNOTHERAPY IN RECURRENT GLIOBLASTOMA

PD-1 checkpoint inhibition has led to remarkable clinical responses in several cancer types. Whereas PD-1 blockade has not shown an overall survival (OS) benefit for glioblastoma (GBM) patients, a subset of them exhibit long-term responses to this immunotherapy. Previously, we reported an enrichment of BRAF/PTPN11 activating mutations in 30% of recurrent GBMs that responded to PD-1 blockade, but the molecular profile of the majority of responders remained elusive. Given that BRAF and PTPN11 promote MAPK/ERK signaling, we investigated whether activation of this pathway is associated with response to PD-1 inhibitors in recurrent GBM, including patients that do not harbor BRAF/PTPN11 mutations. Immunohistochemistry for ERK1/2 phosphorylation (p-ERK), a marker of MAPK/ERK pathway activation, was performed in a discovery cohort including pre-treatment specimens of 29 recurrent GBM patients treated with adjuvant PD-1 blockade, and 33 patients who did not undergo immunotherapy. p-ERK was predictive of response and OS following PD-1 blockade. Yet p-ERK was not associated with OS in patients not treated with immunotherapy. p-ERK was also associated with OS in a validation GBM cohort treated with adjuvant anti-PD-1 therapy. Single-cell RNA-seq and multiplex-immunofluorescence analyses revealed that p-ERK was mainly localized in tumor cells and high p-ERK GBMs contained tumor-infiltrating myeloid cells and microglia with elevated expression of MHC class II and associated genes. Thus, our findings indicate that ERK1/2 activation in recurrent GBM is predictive of response to PD-1 blockade and is associated with a distinct myeloid cell phenotype.

IMMU-43. IMMUNE CONTEXTURE OF ISOCITRATE DEHYDROGENASE STRATIFIED HUMAN GLIOMAS REVEALED BY SINGLE-CELL TRANSCRIPTOMICS AND ACCESSIBLE CHROMATIN

The immune cell composition of isocitrate dehydrogenase wild type (IDH-wt) glioma patients significantly differs compared to IDH-mutant (IDH-mut) yet a detailed and unbiased understanding of their transcriptomic and epigenetic landscapes remains elusive. To this end, we performed single-cell RNA-sequencing (scRNA-seq) and single-cell Assay for Transposase-Accessible Chromatin using sequencing (sc-ATAC-seq) on ~100,000 tumor-associated immune cells from seventeen IDH mutation classified primary and recurrent human gliomas and non-glioma brains (NGBs). Our analyses revealed sixty-two transcriptionally distinct myeloid and lymphoid cell states within and across glioma subtypes and we noted microglial attrition with increasing disease severity concomitant with invading monocyte-derived cells (MDCs) and lymphocytes. Specifically, certain microglial and monocyte-derived subpopulations were associated with antigen presentation gene modules, akin to cross-presenting dendritic cells. As tissue macrophages exhibit multifaceted polarization in response to microenvironmental cues, we clarify the existence of microglia/macrophage functional states beyond M1/M2 paradigms exemplified by the presence of palmitic-, oleic- acid, and glucocorticoid responsive polarized states. We identified cytotoxic T cells with poly-functional cytolytic states mostly in recurrent IDH-wt gliomas. Furthermore, ligand-receptor interactome analyses showed a preponderance of antigen presentation/phagocytosis over the checkpoint axis in IDH-wt compared to IDH-mut gliomas. Additionally, our sc-ATAC-seq analyses revealed differences in regulatory networks in NGBs, IDH-mut, and IDH-wt glioma-associated immune cells. In particular, we noted reduced microglial usage of an iron recycling SPIC transcription factor and Interferon Regulatory Factors (IRFs); IRF1 and IRF2 in IDH-wt relative to IDH-mut and NGBs. Unique features such as amplification of 11-Zinc Finger Protein accessibility were restricted to MDCs. Finally, sc-ATAC-seq profiles of CD8+ exhausted T cells from IDH-wt showed strong enhancer accessibility on CTLA-4, Layilin, and TIM-3 but no enrichment on PD1 was seen. In summary, our study provides unprecedented granular detail of transcriptionally and epigenomically defined glioma-specific immune contexture that can be exploited for immunotherapy applications.

The immune landscape of common CNS malignancies: implications for immunotherapy

Immunotherapy has enabled remarkable therapeutic responses across cancers of various lineages, albeit with some notable exceptions such as glioblastoma. Several previous misconceptions, which have impaired progress in the past, including the presence and role of the blood-brain barrier and a lack of lymphatic drainage, have been refuted. Nonetheless, a subset of patients with brain metastases but, paradoxically, not the vast majority of those with gliomas are able to respond to immune-checkpoint inhibitors. Immune profiling of samples obtained from patients with central nervous system malignancies using techniques such as mass cytometry and single-cell sequencing along with experimental data from genetically engineered mouse models have revealed fundamental differences in immune composition and immunobiology that not only explain the differences in responsiveness to these agents but also lay the foundations for immunotherapeutic strategies that are applicable to gliomas. Herein, we review the emerging data on the differences in immune cell composition, function and interactions within central nervous system tumours and provide guidance on the development of novel immunotherapies for these historically difficult-to-treat cancers.

Circadian regulation of cancer cell and tumor microenvironment crosstalk

Circadian rhythms regulate a remarkable variety of physiologic functions in living organisms. Circadian disruption is associated with tumorigenesis and tumor progression through effects on cancer cell biological properties, including proliferation, DNA repair, apoptosis, metabolism, and stemness. Emerging evidence indicates that circadian clocks also play an influential role in the tumor microenvironment (TME). This review outlines recent discoveries on how cancer cell clock components (including circadian clock and clock genes/proteins) regulate TME biology and, reciprocally, how TME clock components affect tumor growth, metastasis, and therapeutic response. An improved understanding of how clock components regulate the symbiosis between cancer cells and the TME will inform the development of novel clock-oriented therapeutic strategies, including immunotherapy.

Replication stress response defects are associated with response to immune checkpoint blockade in nonhypermutated cancers

[Figure: see text].

American Society of Clinical Oncology 2021 Annual Meeting updates on primary brain tumors and CNS metastatic tumors

In this report, select key studies presented at the American Society of Clinical Oncology (ASCO) 2021 annual meeting are reviewed. Two major phase III randomized controlled trials were presented at the meeting: GEINO 1401 and EORTC 1709/CCTG CE.8. Both are reviewed in this report. Moreover, important phase II trials, including Alliance A0716701, and key phase I trials are included. All trials presented cover important advances in the understanding of primary brain tumor management. In addition, case series papers, trials in progress and select work on exploratory CSF biomarkers are reviewed. Altogether, research presented at ASCO 2021 highlights important advances in neuro-oncologic topics that may inform future research and practice.

New Approaches to Glioblastoma

Faced with unique immunobiology and marked heterogeneity, treatment strategies for glioblastoma require therapeutic approaches that diverge from conventional oncological strategies. The selection and prioritization of targeted and immunotherapeutic strategies will need to carefully consider these features and companion biomarkers developed alongside treatment strategies to identify the appropriate patient populations. Novel clinical trial strategies that interrogate the tumor microenvironment for drug penetration and target engagement will inform go/no-go later-stage clinical studies. Innovative trial designs and analyses are needed to move effective agents toward regulatory approvals more rapidly. Expected final online publication date for the Annual Review of Medicine, Volume 73 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Intratumoral Delivery of STING Agonist Results in Clinical Responses in Canine Glioblastoma

PURPOSE

Activation of STING (stimulator of interferon genes) can trigger a robust, innate antitumor immune response in immunologically "cold" tumors such as glioblastoma.

PATIENTS AND METHODS

A small-molecule STING agonist, IACS-8779, was stereotactically administered using intraoperative navigation intratumorally in dogs with spontaneously arising glioblastoma. The phase I trial used an escalating dose design, ascending through four dose levels (5-20 μg). Treatment was repeated every 4-6 weeks for a minimum of two cycles. Radiographic response to treatment was determined by response assessment in neuro-oncology (RANO) criteria applied to isovoxel postcontrast T1-weighted MR images obtained on a single 3T magnet.

RESULTS

Six dogs were enrolled and completed ≥1 cycle of treatment. One dog was determined to have an abscess and was removed from further analysis. One procedure-related fatality was observed. Radiographic responses were dose dependent after the first cycle. The first subject had progressive disease, whereas there was 25% volumetric reduction in one subject and greater than 50% in the remaining surviving subjects. The median progression-free survival time was 14 weeks (range: 0-22 weeks), and the median overall survival time was 32 weeks (range: 11-39 weeks).

CONCLUSIONS

Intratumoral STING agonist (IACS-8779) administration was well tolerated in dogs with glioblastoma to a dose of 15 μg. Higher doses of IACS-8779 were associated with radiographic responses.

CD11c+CD163+ Cells and Signal Transducer and Activator of Transcription 3 (STAT3) Expression Are Common in Melanoma Leptomeningeal Disease

Leptomeningeal disease (LMD) in melanoma patients is associated with significant neurological sequela and has a dismal outcome, with survival measured typically in weeks. Despite the therapeutic benefit of targeted therapies and immunotherapies for Stage IV melanoma, patients with LMD do not typically benefit. A deeper understanding of the tumor microenvironment (TME) of LMD may provide more appropriate therapeutic selection. A retrospective analysis of subjects who underwent surgical resection with LMD (n=8) were profiled with seven color multiplex staining to evaluate the expression of the global immune suppressive hub - the signal transducer and activator of transcription 3 (STAT3) and for the presence of CD3+ T cells, CD68+ monocyte-derived cells, CD163+ immune suppressive macrophages, and CD11c+ cells [potential dendritic cells (DCs)] in association with the melanoma tumor marker S100B and DAPI for cellular nuclear identification. High-resolution cellular imaging and quantification was conducted using the Akoya Vectra Polaris. CD11c+ cells predominate in the TME (10% of total cells), along with immunosuppressive macrophages (2%). Another potential subset of DCs co-expressing CD11c+ and the CD163+ immunosuppressive marker is frequently present (8/8 of specimens, 8%). Occasional CD3+ T cells are identified, especially in the stroma of the tumor (p=0.039). pSTAT3 nuclear expression is heterogeneous in the various immune cell populations. Occasional immune cluster interactions can be seen in the stroma and on the edge. In conclusion, the TME of LMD is largely devoid of CD3+ T cells but is enriched in immune suppression and innate immunity.

NMR Spectroscopy-Based Metabolomics of Platelets to Analyze Brain Tumors

“Tumor-educated platelets” have recently generated substantial interest for the diagnosis of cancer. We hypothesized that tumor educated platelets from patients with brain tumors will reflect altered metabolism compared to platelets from healthy volunteers. Here, in a pilot study, we have employed nuclear magnetic resonance (NMR) spectroscopy in platelets from brain tumor patients to demonstrate altered metabolism compared to the platelets obtained from healthy volunteers.

Immune Modulatory Short Noncoding RNAs Targeting the Glioblastoma Microenvironment

Glioblastomas are heterogeneous and have a poor prognosis. Glioblastoma cells interact with their neighbors to form a tumor-permissive and immunosuppressive microenvironment. Short noncoding RNAs are relevant mediators of the dynamic crosstalk among cancer, stromal, and immune cells in establishing the glioblastoma microenvironment. In addition to the ease of combinatorial strategies that are capable of multimodal modulation for both reversing immune suppression and enhancing antitumor immunity, their small size provides an opportunity to overcome the limitations of blood-brain-barrier (BBB) permeability. To enhance glioblastoma delivery, these RNAs have been conjugated with various molecules or packed within delivery vehicles for enhanced tissue-specific delivery and increased payload. Here, we focus on the role of RNA therapeutics by appraising which types of nucleotides are most effective in immune modulation, lead therapeutic candidates, and clarify how to optimize delivery of the therapeutic RNAs and their conjugates specifically to the glioblastoma microenvironment.

Qki is an essential regulator of microglial phagocytosis in demyelination

The mechanism underpinning the regulation of microglial phagocytosis in demyelinating diseases is unclear. Here, we showed that the Quaking protein (Qki) in microglia was greatly induced by demyelination in the brains of both mice and humans. Deletion of the Quaking gene (Qk) in microglia severely impaired the clearance of myelin debris. Transcriptomic profiling indicated that depletion of Qki impaired total RNA levels and splicing of the genes involved in phagosome formation and maturation. RNA immunoprecipitation (RIP) confirmed the physical interactions between the Qki protein and the mRNAs of Qki targets that are involved in phagocytosis, indicating that Qki regulates their RNA stability. Both Qki depletion and inhibition of Qki target Cd36 greatly reduced the phagocytic activity of microglia and macrophages. The defective uptake and degradation of myelin debris caused by Qki depletion in microglia resulted in unresolved myelin debris that impaired axon integrity, oligodendrocyte maturation, and subsequent remyelination. Thus, our results demonstrate that Qki is an essential regulator of microglia’s phagocytic activity under demyelinating conditions.

LMD-20. Immune Suppressive Macrophages and Signal Transducer and Activator of Transcription 3 (STAT3) Expression are common in Melanoma Leptomeningeal Disease

Leptomeningeal disease (LMD) in melanoma patients is associated with significant neurological impairments and has a dismal outcome with a median survival of 1.8 months. Despite the therapeutic benefit of targeted therapies and immunotherapies for most kinds of Stage IV melanoma, patients with LMD do not typically benefit. A deeper understanding of the tumor microenvironment (TME) of LMD may provide more appropriate therapeutic selection. A retrospective analysis of subjects who underwent surgical resection with LMD (n=8) were profiled with seven color multiplex to evaluate the expression of the global immune suppressive hub - the signal transducer and activator of transcription 3 (STAT3) and for the presence of CD3 T cells, CD68+ monocytes, CD163 immune suppressive macrophages, CD11c+ antigen presenting cells (APCs) in association with the melanoma tumor marker S100B and DAPI for cellular nuclear identification. High-resolution cellular imaging and quantification was conducted using the Akoya Vectra Polaris. CD163+ macrophage is the most frequent immune cell population in the LMD TME. Occasional CD3+ T cells and CD11c+ APC are also identified, although the latter has concurrent expression of CD163. STAT3 nuclear localization is heterogeneously expressed in the various immune cell populations. Occasional immune cluster interactions can be seen in the tumor stroma and the tumor edge. In conclusion, the TME of LMD is largely devoid of CD3+ T cells, but is enriched for immune suppression and innate immunity.

Immune Microenvironment Landscape in CNS Tumors and Role in Responses to Immunotherapy

Despite the important evolution of immunotherapeutic agents, brain tumors remain, in general, refractory to immune therapeutics. Recent discoveries have revealed that the glioma microenvironment includes a wide variety of immune cells in various states that play an important role in the process of tumorigenesis. Anti-tumor immune activity may be occurring or induced in immunogenic hot spots or at the invasive edge of central nervous system (CNS) tumors. Understanding the complex heterogeneity of the immune microenvironment in gliomas will likely be the key to unlocking the full potential of immunotherapeutic strategies. An essential consideration will be the induction of immunological effector responses in the setting of the numerous aspects of immunosuppression and evasion. As such, immune therapeutic combinations are a fundamental objective for clinical studies in gliomas. Through immune profiling conducted on immune competent murine models of glioma and ex vivo human glioma tissue, we will discuss how the frequency, distribution of immune cells within the microenvironment, and immune modulatory processes, may be therapeutically modulated to lead to clinical benefits.

A prospective phase II randomized trial of proton radiotherapy vs intensity-modulated radiotherapy for patients with newly diagnosed glioblastoma

BACKGROUND

To determine if proton radiotherapy (PT), compared to intensity-modulated radiotherapy (IMRT), delayed time to cognitive failure in patients with newly diagnosed glioblastoma (GBM).

METHODS

Eligible patients were randomized unblinded to PT vs IMRT. The primary endpoint was time to cognitive failure. Secondary endpoints included overall survival (OS), intracranial progression-free survival (PFS), toxicity, and patient-reported outcomes (PROs).

RESULTS

A total of 90 patients were enrolled and 67 were evaluable with median follow-up of 48.7 months (range 7.1-66.7). There was no significant difference in time to cognitive failure between treatment arms (HR, 0.88; 95% CI, 0.45-1.75; P = .74). PT was associated with a lower rate of fatigue (24% vs 58%, P = .05), but otherwise, there were no significant differences in PROs at 6 months. There was no difference in PFS (HR, 0.74; 95% CI, 0.44-1.23; P = .24) or OS (HR, 0.86; 95% CI, 0.49-1.50; P = .60). However, PT significantly reduced the radiation dose for nearly all structures analyzed. The average number of grade 2 or higher toxicities was significantly higher in patients who received IMRT (mean 1.15, range 0-6) compared to PT (mean 0.35, range 0-3; P = .02).

CONCLUSIONS

In this signal-seeking phase II trial, PT was not associated with a delay in time to cognitive failure but did reduce toxicity and patient-reported fatigue. Larger randomized trials are needed to determine the potential of PT such as dose escalation for GBM and cognitive preservation in patients with lower-grade gliomas with a longer survival time.

Targeting the Tumor Microenvironment in Brain Metastasis

Dynamic interplay between cancer cells and the surrounding microenvironment is a feature of the metastatic process. Successful metastatic brain colonization requires complex mechanisms that ultimately allow tumor cells to adapt to the unique microenvironment of the central nervous system, evade immune destruction, survive, and grow. Accumulating evidence suggests that components of the brain tumor microenvironment (TME) play a vital role in the metastatic cascade. In this review, the authors summarize the contribution of the TME to the development and progression of brain metastasis. They also highlight opportunities for TME-directed targeted therapy.

Targeting the αv integrin/TGF-β axis improves natural killer cell function against glioblastoma stem cells

Glioblastoma multiforme (GBM), the most aggressive brain cancer, recurs because glioblastoma stem cells (GSCs) are resistant to all standard therapies. We showed that GSCs, but not normal astrocytes, are sensitive to lysis by healthy allogeneic natural killer (NK) cells in vitro. Mass cytometry and single-cell RNA sequencing of primary tumor samples revealed that GBM tumor-infiltrating NK cells acquired an altered phenotype associated with impaired lytic function relative to matched peripheral blood NK cells from patients with GBM or healthy donors. We attributed this immune evasion tactic to direct cell-to-cell contact between GSCs and NK cells via αv integrin-mediated TGF-β activation. Treatment of GSC-engrafted mice with allogeneic NK cells in combination with inhibitors of integrin or TGF-β signaling or with TGFBR2 gene-edited allogeneic NK cells prevented GSC-induced NK cell dysfunction and tumor growth. These findings reveal an important mechanism of NK cell immune evasion by GSCs and suggest the αv integrin/TGF-β axis as a potentially useful therapeutic target in GBM.

OTME-23. Single-cell transcriptomic and epigenomic immune landscape of isocitrate dehydrogenase stratified human gliomas

The brain tumor immune microenvironment (TIME) continuously evolves during glioma progression, but a comprehensive characterization of the glioma-centric immune cell repertoire beyond a priori cell states is uncharted. In this study, we performed single-cell RNA-sequencing (scRNA-seq) and single cell- Assay for Transposase-Accessible Chromatin using sequencing (sc-ATAC-seq) on ~100,000 tumor-associated immune cells from seventeen isocitrate dehydrogenase (IDH) mutation classified primary and recurrent human gliomas and non-glioma brains (NGBs). Our analyses revealed sixty-two transcriptionally distinct myeloid and lymphoid cell states within and across glioma subtypes and we noted microglial attrition with increasing disease severity concomitant with invading monocyte-derived cells and lymphocytes. Specifically, certain microglial and monocyte-derived subpopulations were associated with antigen presentation gene modules, akin to cross-presenting dendritic cells (DCs). We identified cytotoxic T cells with poly-functional cytolytic states mostly in recurrent IDH-wt gliomas. Furthermore, ligand-receptor interactome analyses showed a preponderance of antigen presentation and phagocytosis over the checkpoint axis in IDH-wt compared to IDH-mut gliomas.

Additionally, our sc-ATAC-seq analyses revealed differences in regulatory networks in NGBs, IDH-mut and IDH-wt glioma associated immune cells. In particular, we noted abundant usage of inflammatory transcription factors (TFs) as exemplified by Nuclear factor kappa B and Activator Protein-1 TF family in IDH-wt microglia when compared with microglia from IDH-mut and NGBs. Unique features such as amplification of 11- Zinc Finger Protein accessibility were restricted to monocyte derived cells and were not observed in microglia. Finally, sc-ATAC-seq profiles of CD8⁺ exhausted T cells from IDH-wt showed strong enhancer accessibility on Cytotoxic T-lymphocyte-associated protein 4, Layilin and Hepatitis A Virus Cellular Receptor 2 but no enrichment on PDCD1 (gene encoding Programmed cell death protein 1) was seen. In summary, our study provides unprecedented granular detail of transcriptionally defined glioma- specific immune contexture that can be exploited for immunotherapy applications.

This study in K.B. laboratory was supported by the generous philanthropic contributions to The University of Texas (UT) MD Anderson Cancer Center (MDACC) Moon Shots Program™, Marnie Rose Foundation, NIH grants: R21 CA222992 and R01CA225963. This study was partly supported by the UT MDACC start-up research fund to L.W. and CPRIT Single Core grant RP180684 to N. E. N.

Systematic review of combinations of targeted or immunotherapy in advanced solid tumors

With rapid advances in our understanding of cancer, there is an expanding number of potential novel combination therapies, including novel-novel combinations. Identifying which combinations are appropriate and in which subpopulations are among the most difficult questions in medical research. We conducted a Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA)-guided systematic review of trials of novel-novel combination therapies involving immunotherapies or molecular targeted therapies in advanced solid tumors. A MEDLINE search was conducted using a modified Cochrane Highly Sensitive Search Strategy for published clinical trials between July 1, 2017, and June 30, 2020, in the top-ranked medical and oncology journals. Trials were evaluated according to a criterion adapted from previously published Food and Drug Administration guidance and other key considerations in designing trials of combinations. This included the presence of a strong biological rationale, the use of a new established or emerging predictive biomarker prospectively incorporated into the clinical trial design, appropriate comparator arms of monotherapy or supportive external data sources and a primary endpoint demonstrating a clinically meaningful benefit. Of 32 identified trials, there were 11 (34%) trials of the novel-novel combination of anti-programmed death 1 (PD-1)/programmed death ligand 1 (PD-L1) and anti-cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) therapy, and 10 (31%) trials of anti-PD-1/PD-L1 and anti-vascular endothelial growth factor (VEGF) combination therapy. 20 (62.5%) trials were phase II trials, while 12 (37.5%) were phase III trials. Most (72%) trials lacked significant preclinical evidence supporting the development of the combination in the given indication. A majority of trials (69%) were conducted in biomarker unselected populations or used pre-existing biomarkers within the given indication for patient selection. Most studies (66%) were considered to have appropriate comparator arms or had supportive external data sources such as prior studies of monotherapy. All studies were evaluated as selecting a clinically meaningful primary endpoint. In conclusion, designing trials to evaluate novel-novel combination therapies presents numerous challenges to demonstrate efficacy in a comprehensive manner. A greater understanding of biological rationale for combinations and incorporating predictive biomarkers may improve effective evaluation of combination therapies. Innovative statistical methods and increasing use of external data to support combination approaches are potential strategies that may improve the efficiency of trial design. Designing trials to evaluate novel-novel combination therapies presents numerous challenges to demonstrate efficacy in a comprehensive manner. A greater understanding of biological rationale for combinations and incorporating predictive biomarkers may improve effective evaluation of combination therapies. Innovative statistical methods and increasing use of external data to support combination approaches are potential strategies that may improve the efficiency of trial design.

Abstract 1492: Chimeric antigen receptor (CAR) T cell donor dependent dysfunction modulation with activation of autophagy and inhibition of trogocytosis

Introduction: Effective anti-tumor immunity requires the presence of abundant effector T cells in the tumor microenvironment with both cancer cell specificity and cytotoxic potency. Chimeric antigen receptor (CAR) T cells engineered ex vivo to fulfill such quintessence are effective in both experimental and clinical settings with curative potential. However, the efficacy of CAR T cells can be limited by trogocytosis whereby CAR T cells extract cognate antigens from target cells thereby eliciting antigen escape and then express the target antigen on the CAR triggering fratricide that reduces the CAR persistence and efficacy.

Methods: Epidermal growth factor variant III (EGFRvIII) specific CAR T cells were generated from various donors and analyzed for EGFRvIII cytotoxicity, trogocytosis, and in vivo therapeutic activity which was modulated with verteporfin, an inducer of autophagy and bafilomycin A1, an inhibitor of autophagy. A three-way co-culture system modeling the glioblastoma microenvironment of the CAR T cell interaction with targets (U87-EGFRvIII) and bystanders (U87-EGFR) was used to evaluate phagocytic and autophagy functions of the CAR T cells.

Results: Glioblastoma-specific EGFRvIII CARs induce trogocytosis of the cognate tumor antigen upon engaging target tumor cells within 2 hours. Trogocytic activity varies in a donor-dependent manner and correlates with impaired CAR performance in murine models of orthotopic gliomas expressing EGFRvIII. Trogocytosis is blocked with verteporfin which restores cytolytic capacity of the CAR. In the three-way co-culture system, therapeutically effective in vivo CARs demonstrate superior phagocytic clearance of U87-EGFRvIII released mitochondria that is blocked by autophagy inhibition. The induction of immune checkpoints such as PD-L1 during CAR-target interaction is enhanced when autophagy is blocked. Furthermore, autophagy blockade prevents phagocytic clearance of cytolytic target release of mitochondria. We further demonstrate that pharmacological facilitation of autophagy with verteporfin inhibits trogocytic expression of target tumor antigen on CARs and thereby markedly increases CAR persistence in the glioma microenvironment in mice.

Conclusions: Our data establish autophagy as an antagonizing mechanism counteracting CAR-induced trogocytosis and immune checkpoint activation, providing evidence for a new strategy to innovate high-performance CARs.

Citation Format: Jiyong Liang, Dexing Fang, Amy B. Heimberger. Chimeric antigen receptor (CAR) T cell donor dependent dysfunction modulation with activation of autophagy and inhibition of trogocytosis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1492.

Abstract 1553: Intratumoral delivery of STING agonist results in radiographic response in spontaneous canine high-grade glioma

Introduction: STING (stimulator of interferon genes) agonists can increase T cell infiltration into immunologically “cold” tumors such as gliomas through proinflammatory activation of suppressive tumor stroma, re-education of tumor-supportive M2 macrophages toward a proinflammatory M1 phenotype and can reverse the suppressive phenotype of myeloid-derived suppressor cells. Preclinical murine glioma models have not correlated with immunotherapy responses in human glioma subjects in part because of poor correlative immunobiology, but recent “omic” profiling has demonstrated a marked association of spontaneously arising canine gliomas with those in human subjects.

Methods: We have created a novel STING agonist IACS-8779 that has shown robust activation of the STING pathway with equivalent or superior systemic anti-tumor responses relative to clinical benchmark compounds in murine models. A dose escalation clinical trial was conducted in client-owned canines (n=4) with newly-diagnosed presumed high-grade glioma identified radiographically on standard MRI sequences obtained on a 3T magnet. Each dog received 2 injections intratumorally at an interval of 4-6 weeks. The dose of IACS-8779 was sequentially increased over the course of the 6 injections from 5ug to 20ug, whereas the injection volume was fixed at 50uL. Injections were targeted to the tumors by image guidance, and injections were performed at a rate of 2uL/minute. Neurological status was monitored during the inter-injection interval. MRI was repeated at intervals of 4-6 weeks and radiographic responses were volumetrically analyzed.

Results: All dogs tolerated the injections well with clinical symptoms remaining stable between the first and second injection. The survival times of the first 2 dogs were 2.5 and 9 months from the date of onset of signs, whereas the remaining dogs are still alive. The first dog, treated twice at a dose of 5ug, had progressive disease on serial MRI; whereas the second (5 and 10ug) and third (15 and 20ug) dogs had stable disease. The fourth dog treated at 20ug showed a volumetric change of 0.785cm3 pre-treatment to 0.194cm3 (>75%) after a single dose 5 weeks after the first injection.

Conclusion: In support of previously published data showing effectiveness of IACS-8779 for treatment of orthotopic murine tumors (Ager CR, Bioorg Med Chem Lett. 2019), these data indicate that IACS-8779 is well-tolerated for repeated intratumoral injections up to 20ug in 50uL in a large animals (canines) with spontaneous glioma. Further, we have shown that a single injection of 20ug IACS-8779 can produce a radiographic response in a spontaneously arising high-grade glioma in the dog.

Citation Format: C. Elizabeth Boudreau, Cynthia Kassab, Martina Ott, Chase M. DeRay, Jonathan Levine, Michael Curran, Amy B. Heimberger. Intratumoral delivery of STING agonist results in radiographic response in spontaneous canine high-grade glioma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1553.

Abstract 1489: Deposition of genetically engineered T cell attracting antigen presenting cells in the glioma microenvironment with low intensity pulsed ultrasound-based blood-brain barrier opening triggers therapeutic responses in preclinical glioma models

Introduction: In contrast to brain metastases, gliomas have few antigen-presenting cells (APCs) in the tumor microenvironment, which may limit T cell effector responses. We hypothesized that: (1) an APC could be modified to express a T cell attracting chemokine that could enhance localized immune activation, and (2) that ultrasound-based blood-brain barrier (BBB) opening would enhance delivery of these APCs at the site of tumor antigens.

Methods: Murine F4/80 and CD11c expressing APCs were isolated from the bone marrow of C57BL/6 mice and modified via lentiviral transduction to encode the cDNA of immune cell chemokines CXCL9 or CXCL10 and methionine-deficient green fluorescent protein (co-expression) for cell tagging. C57BL/6 mice were implanted with GL261 cells and treated with 1 x 106 CXCL9 or CXCL10 over-expressing APCs intracranially (i.c.), or intravenously (i.v.) with or without ultrasound-based BBB opening. To determine how the CXCL10 expressing APCs were altering the tumor microenvironment, immune cells were isolated from the glioma implanted hemisphere of all treatment groups and analyzed by multicolor flow cytometry.

Results: Transduced APCs produced 3,392 pg/ml and 2,987 pg/ml of CXCL9 or CXCL10, respectively. Mice tolerated the treatments well without any adverse events, behavioral changes, or neurological toxicity. Survival analysis of mice treated with CXCL9 expressing APCs using i.c., or i.v. with and without BBB opening ultrasound showed no significant survival benefit compared with PBS-treated control mice. Mice treated i.c. with CXCL10-expressing APCs had significantly improved survival relative to the PBS control group (p<0.05), demonstrating that this cellular therapy required access to the tumor microenvironment in order to be effective. Notably, the most therapeutically efficacious administration route was when the CXCL10-expressing APCs were administered i.v. before ultrasound-based BBB opening even relative to the i.c. administered group (p<0.05). Intravenous administration of CXCL10 APCs combined with ultrasound-based BBB opening also significantly increased the percentage of T cells in the glioma microenvironment relative to all other treatment groups.

Conclusions: The delivery of CXCL10-secreting APCs to the glioma microenvironment with ultrasound-based BBB opening was superior to delivery with direct i.c. injection. BBB disruption may have triggered more diffuse dispersal of the APCs throughout the tumor microenvironment or positioned these cells in closer proximity to the T cells emigrating from the vascular space into the localized glioma microenvironment.

Citation Format: Aria Sabbagh, Kevin Beccaria, Xiaoyang Ling, Anantha Marisetty, Martina Ott, Ling-Yuan Kong, Dexing Fang, Jun Wei, Carole Desseaux, Guillaume Bouchoux, Michael Canney, Alexandre Carpentier, Amy B. Heimberger. Deposition of genetically engineered T cell attracting antigen presenting cells in the glioma microenvironment with low intensity pulsed ultrasound-based blood-brain barrier opening triggers therapeutic responses in preclinical glioma models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1489.

Gliosarcoma vs. glioblastoma: a retrospective case series using molecular profiling

Background

Gliosarcoma (GS) refers to the presence of mesenchymal differentiation (as seen using light microscopy) in the setting of glioblastoma (GB, an astrocytoma, WHO Grade 4). Although the same approach to treatment is typically adopted for GS and GB, there remains some debate as to whether GS should be considered a discrete pathological entity. Differences between these tumors have not been clearly established at the molecular level.

Methods

Patients with GS (n=48) or GB (n=1229) underwent molecular profiling (MP) with a pan-cancer panel of tests as part of their clinical care. The methods employed included next-generation sequencing (NGS) of DNA and RNA, copy number variation (CNV) of DNA and immunohistochemistry (IHC). The MP comprised 1153 tests in total, although results for each test were not available for every tumor profiled. We analyzed this data retrospectively in order to determine if our results were in keeping with what is known about the pathogenesis of GS by contrast with GB. We also sought novel associations between the MP and GS vs. GB which might improve our understanding of pathogenesis of GS.

Results

Potentially meaningful associations (p<0.1, Fisher’s exact test (FET)) were found for 14 of these tests in GS vs. GB. A novel finding was higher levels of proteins mediating immuno-evasion (PD-1, PD-L1) in GS. All of the differences we observed have been associated with epithelial-to-mesenchymal transition (EMT) in other tumor types. Many of the changes we saw in GS are novel in the setting of glial tumors, including copy number amplification in LYL1 and mutations in PTPN11.

Conclusions

GS shows certain characteristics of EMT, by contrast with GB. Treatments targeting immuno-evasion may be of greater therapeutic value in GS relative to GB.

Supplementary Information

The online version contains supplementary material available at (10.1186/s12883-021-02233-5).

Phase II trial of proton therapy versus photon IMRT for GBM: secondary analysis comparison of progression-free survival between RANO versus clinical assessment

Background

This secondary image analysis of a randomized trial of proton radiotherapy (PT) versus photon intensity-modulated radiotherapy (IMRT) compares tumor progression based on clinical radiological assessment versus Response Assessment in Neuro-Oncology (RANO).

Methods

Eligible patients were enrolled in the randomized trial and had MR imaging at baseline and follow-up beyond 12 weeks from completion of radiotherapy. “Clinical progression” was based on a clinical radiology report of progression and/or change in treatment for progression.

Results

Of 90 enrolled patients, 66 were evaluable. Median clinical progression-free survival (PFS) was 10.8 (range: 9.4–14.7) months; 10.8 months IMRT versus 11.2 months PT (P = .14). Median RANO-PFS was 8.2 (range: 6.9, 12): 8.9 months IMRT versus 6.6 months PT (P = .24). RANO-PFS was significantly shorter than clinical PFS overall (P = .001) and for both the IMRT (P = .01) and PT (P = .04) groups. There were 31 (46.3%) discrepant cases of which 17 had RANO progression more than a month prior to clinical progression, and 14 had progression by RANO but not clinical criteria.

Conclusions

Based on this secondary analysis of a trial of PT versus IMRT for glioblastoma, while no difference in PFS was noted relative to treatment technique, RANO criteria identified progression more often and earlier than clinical assessment. This highlights the disconnect between measures of tumor response in clinical trials versus clinical practice. With growing efforts to utilize real-world data and personalized treatment with timely adaptation, there is a growing need to improve the consistency of determining tumor progression within clinical trials and clinical practice.

Opening of the Blood-Brain Barrier Using Low-Intensity Pulsed Ultrasound Enhances Responses to Immunotherapy in Preclinical Glioma Models

PURPOSE

The blood-brain barrier (BBB) inhibits adequate dosing/penetration of therapeutic agents to malignancies in the brain. Low-intensity pulsed ultrasound (LIPU) is a safe therapeutic method of temporary BBB disruption (BBBD) to enhance chemotherapeutic delivery to the tumor and surrounding brain parenchyma for treatment of glioblastoma.

EXPERIMENTAL DESIGN

We investigated if LIPU could enhance therapeutic efficacy of anti-PD-1 in C57BL/6 mice bearing intracranial GL261 gliomas, epidermal growth factor receptor variant III (EGFRvIII) chimeric antigen receptor (CAR) T cells in NSG mice with EGFRvIII-U87 gliomas, and a genetically engineered antigen-presenting cell (APC)-based therapy producing the T-cell attracting chemokine CXCL10 in the GL261-bearing mice.

RESULTS

Mice treated with anti-PD-1 and LIPU-induced BBBD had a median survival duration of 58 days compared with 39 days for mice treated with anti-PD-1, and long-term survivors all remained alive after contralateral hemisphere rechallenge. CAR T-cell administration with LIPU-induced BBBD resulted in significant increases in CAR T-cell delivery to the CNS after 24 (P < 0.005) and 72 (P < 0.001) hours and increased median survival by greater than 129%, in comparison with CAR T cells alone. Local deposition of CXCL10-secreting APCs in the glioma microenvironment with LIPU enhanced T-cell glioma infiltration during the therapeutic window (P = 0.004) and markedly enhanced survival (P < 0.05).

CONCLUSIONS

LIPU increases immune therapeutic delivery to the tumor microenvironment with an associated increase in survival and is an emerging technique for enhancing novel therapies in the brain.

Intrathecal (IT) and intravenous (IV) nivolumab (N) for metastatic melanoma (MM) patients (pts) with leptomeningeal disease (LMD)

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Background: MM pts with LMD have a dismal prognosis, with median overall survival (OS) < 3 months, no approved therapies and extremely limited clinical trial options. We previously reported initial safety findings from an open label, single arm, single center phase I/IB trial (NCT03025256), in which IT and IV N were well tolerated, without any CNS-specific or unexpected toxicity. Here we report an update on safety and maximum tolerated dose (MTD) for all patients enrolled, and efficacy for the completed dose cohorts. Methods: MM patients aged >18 with evidence of LMD by MRI and/or CSF cytology, ECOG PS ≤2 were treated with IT and IV N. Dexamethasone ≤4mg/daily and concurrent BRAF/MEK inhibitor(i) treatment was allowed. For cycle 1, IT N was administered via intraventricular reservoir on day (D)1. For subsequent cycles (every 14 days), pts received IT N on D1, followed by IV N 240 mg on D2. IT N doses evaluated were 5, 10, 20 mg and 50 mg. Blood and CSF were collected at multiple time points for translational research. The primary objectives of this first-in-human study were to determine the safety and MTD of IT N given with IV N in MM pts with LMD. Bayesian mTPI methodology was used to define the MTD. Results: To date, 23 pts have been treated: two at 5, three at 10, fourteen at 20 mg and four at 50 mg IT N. Median age at LMD diagnosis was 42 (28-73); 12 pts are male. All pts had radiographic evidence of LMD and neurological symptoms; 14 pts had positive CSF cytology at baseline. 21 pts received prior therapies for their metastatic melanoma: anti-PD1 (n = 19), BRAFi/MEKi (n = 14), chemo (n = 2), IT IL2 (n = 4) other (n = 2). 19 pts had prior XRT, including whole brain RT (n = 7). Two pts were treatment-naïve. The median number of IT N doses was five (1- 66). The combination regimen was well tolerated by all evaluable pts (n=23), with only five pts (22%) experiencing gr 3 AEs, and no reported gr 4 or 5 toxicities. Nausea (30%), diarrhea (26%), and rash (22%) were the most common AEs. Eight pts (23%) experienced AEs after IT N administration, all gr 1. Initial efficacy analysis included only pts (n=19) treated with first three dose levels (5-20mg). Median follow-up for these pts is 4.5 months (mos) (1.1, 31.5 mos) and median OS is 63 % at 3 mos, 42 % at 6 mos and 30% at 12 mos. Conclusions: The trial demonstrates the feasibility and safety of IT administration of modern immunotherapy for MM pts with LMD. No unexpected systemic or neurological toxicity was observed with 20mg IT N. 2 additional patients are required to complete the 50mg IT N cohort. OS rates at 6 and 12 mos are encouraging and support further evaluation of IT administration of immunotherapy agents for pts with MM and LMD. Final presentation will include results of LMD for all dose cohorts, composite response assessment and comparative analysis of longitudinal CSF samples to assess immunologic effects. Clinical trial information: NCT03025256.

Stereotactic radiosurgery (SRS) for brain metastasis (BM) in hormone receptor positive (HR+) HER2 negative breast cancer (BC)

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Background: With the increase of the utilization of SRS for the treatment of oligometastatic BM over surgical reaction or whole brain radiation therapy (WBRT), we sought to evaluate the impact of SRS on overall survival in HR+Her2- BC and prognostic factors associated with SRS. Methods: We reviewed prospectively collected data in the electronic data bases of the breast medical, surgical and radiation oncology departments at MD Anderson cancer center. We aimed at identifying HR+HER2- BC patients who received upfront SRS for BM’s between 08/10/2009 and 02/27/2018.Overall survival was defined as the time from the first SRS to last follow-up/death. Multivariate analysis by the Cox proportional hazards regression analysis was performed to evaluate the prognostic factors (age at BM, stage, Karnofsky performance score (KPS), symptomatic BM, BM at 1stdistant metastatic presentation, extracranial Disease, treatment history, salvage therapy, number of brain lesion treated) of SRS that influenced survival. Results: A total of 125 patients were identified, and we are reporting on 68 with completed analysis. Median age at time of first SRS was 53.86 years. 51 patients of the 68 were deceased at the time of this analysis and 17 patients were alive at the time of last follow-up. 49 patients (72.06 %) presented with radiation necrosis after SRS; 36 patients (52.94 %) presented with BM as 1st distant metastasis including metastasis to other sites. Number of BM’s lesions <4 was 60 (88.2%) and >=4 was 7 (10.3%). The median follow-up from time of first SRS for survivors was 10.84 months. 24 (35.29%) received two or more sessions of SRS and the mean time between first and second SRS sessions for these patients was 14.24 months. Median time from first SRS to second SRS for ER+HER2− patients was 10.84 months (n = 24); on multivariable analysis, higher Karnofsky performance score (KPS) was associated with better survival compared to no salvage therapy. Patients with KPS>90 (p=0.005) had better survival and reduced the hazard by a factor of 0.33 (or 67%). Receiving SRS (p=0.0003) or SRS+WBRT (0.0001) as salvage therapy reduced the hazard (risk of death) by 86% and 85%, respectively. Conclusions: SRS is an effective treatment modality for HR+HER2- BM from BC. Patients who received SRS or SRS and WBRT, KPS >90 had better survival than patients who didn’t receive any salvage therapy. Updated data will be available at the time of the presentation.[Table: see text]

Window-of-opportunity clinical trial of pembrolizumab in patients with recurrent glioblastoma reveals predominance of immune-suppressive macrophages

BACKGROUND

We sought to ascertain the immune effector function of pembrolizumab within the glioblastoma (GBM) microenvironment during the therapeutic window.

METHODS

In an open-label, single-center, single-arm phase II "window-of-opportunity" trial in 15 patients with recurrent (operable) GBM receiving up to 2 pembrolizumab doses before surgery and every 3 weeks afterward until disease progression or unacceptable toxicities occurred, immune responses were evaluated within the tumor.

RESULTS

No treatment-related deaths occurred. Overall median follow-up time was 50 months. Of 14 patients monitored, 10 had progressive disease, 3 had a partial response, and 1 had stable disease. Median progression-free survival (PFS) was 4.5 months (95% CI: 2.27, 6.83), and the 6-month PFS rate was 40%. Median overall survival (OS) was 20 months, with an estimated 1-year OS rate of 63%. GBM patients' recurrent tumors contained few T cells that demonstrated a paucity of immune activation markers, but the tumor microenvironment was markedly enriched for CD68+ macrophages.

CONCLUSIONS

Immune analyses indicated that pembrolizumab anti-programmed cell death 1 (PD-1) monotherapy alone can't induce effector immunologic response in most GBM patients, probably owing to a scarcity of T cells within the tumor microenvironment and a CD68+ macrophage preponderance.

Unique challenges for glioblastoma immunotherapy-discussions across neuro-oncology and non-neuro-oncology experts in cancer immunology. Meeting Report from the 2019 SNO Immuno-Oncology Think Tank

Cancer immunotherapy has made remarkable advances with over 50 separate Food and Drug Administration (FDA) approvals as first- or second-line indications since 2015. These include immune checkpoint blocking antibodies, chimeric antigen receptor-transduced T cells, and bispecific T-cell-engaging antibodies. While multiple cancer types now benefit from these immunotherapies, notable exceptions thus far include brain tumors, such as glioblastoma. As such, it seems critical to gain a better understanding of unique mechanistic challenges underlying the resistance of malignant gliomas to immunotherapy, as well as to acquire insights into the development of future strategies. An Immuno-Oncology Think Tank Meeting was held during the 2019 Annual Society for Neuro-Oncology Scientific Conference. Discussants in the fields of neuro-oncology, neurosurgery, neuro-imaging, medical oncology, and cancer immunology participated in the meeting. Sessions focused on topics such as the tumor microenvironment, myeloid cells, T-cell dysfunction, cellular engineering, and translational aspects that are critical and unique challenges inherent with primary brain tumors. In this review, we summarize the discussions and the key messages from the meeting, which may potentially serve as a basis for advancing the field of immune neuro-oncology in a collaborative manner.

High tumor mutation burden fails to predict immune checkpoint blockade response across all cancer types

BACKGROUND

High tumor mutation burden (TMB-H) has been proposed as a predictive biomarker for response to immune checkpoint blockade (ICB), largely due to the potential for tumor mutations to generate immunogenic neoantigens. Despite recent pan-cancer approval of ICB treatment for any TMB-H tumor, as assessed by the targeted FoundationOne CDx assay in nine tumor types, the utility of this biomarker has not been fully demonstrated across all cancers.

PATIENTS AND METHODS

Data from over 10 000 patient tumors included in The Cancer Genome Atlas were used to compare approaches to determine TMB and identify the correlation between predicted neoantigen load and CD8 T cells. Association of TMB with ICB treatment outcomes was analyzed by both objective response rates (ORRs, N = 1551) and overall survival (OS, N = 1936).

RESULTS

In cancer types where CD8 T-cell levels positively correlated with neoantigen load, such as melanoma, lung, and bladder cancers, TMB-H tumors exhibited a 39.8% ORR to ICB [95% confidence interval (CI) 34.9-44.8], which was significantly higher than that observed in low TMB (TMB-L) tumors [odds ratio (OR) = 4.1, 95% CI 2.9-5.8, P < 2 × 10^-16]. In cancer types that showed no relationship between CD8 T-cell levels and neoantigen load, such as breast cancer, prostate cancer, and glioma, TMB-H tumors failed to achieve a 20% ORR (ORR = 15.3%, 95% CI 9.2-23.4, P = 0.95), and exhibited a significantly lower ORR relative to TMB-L tumors (OR = 0.46, 95% CI 0.24-0.88, P = 0.02). Bulk ORRs were not significantly different between the two categories of tumors (P = 0.10) for patient cohorts assessed. Equivalent results were obtained by analyzing OS and by treating TMB as a continuous variable.

CONCLUSIONS

Our analysis failed to support application of TMB-H as a biomarker for treatment with ICB in all solid cancer types. Further tumor type-specific studies are warranted.

FGL2-wired macrophages secrete CXCL7 to regulate the stem-like functionality of glioma cells

Glioma stem cells (GSCs) are thought to underlie glioma initiation, evolution, resistance to therapies, and relapse. They are defined by their capacity to initiate glioma in immunocompromised mice which precludes analysis of their interaction with immune cells. Macrophages dominate the immune cell composition in glioma. We hypothesized that stemness and immune evasion induced by macrophages are closed intertwined in glioma. By using mass cytometry and RNA sequencing, we reveal that in immunocompetent mice, FGL2 promotes the stem-like phenotypes of glioma cells in an expression level-dependent manner. Mechanistically, FGL2-producing glioma cells recruit macrophages into the tumor microenvironment and induce the macrophages to secrete CXCL7 via the CD16/SyK/PI3K/HIF1α pathways. CXCL7, in turn, enhances the stem-like functionality of glioma cells, resulting in an increase in tumor incidence and progression that can be blocked with a neutralizing anti-CXCL7 antibody. Clinically, the FGL2-CXCL7 paracrine loop positively correlated with a higher macrophage signature and poorer prognosis in glioma patients. Thus, glioma cells' stem-like functionality is regulated by FGL2 in the presence of macrophages, and the FGL2-CXCL7 paracrine signaling axis is critical for regulating this function.

Context-Dependent Glioblastoma-Macrophage/Microglia Symbiosis and Associated Mechanisms

Glioblastoma (GBM) is a lethal form of primary brain tumor in human adults. The impact of tumor-intrinsic alterations is not exclusively confined to cancer cells but can also be extended to the tumor microenvironment (TME). Glioblastoma-associated macrophages/microglia (GAMs) are a prominent type of immune cells that account for up to 50% of total cells in GBM. Emerging evidence suggests that context-dependent GBM-GAM symbiotic interactions are pivotal for tumor growth and progression. Here, we discuss how specific genetic alterations in GBM cells affect GAM biology and, reciprocally, how GAMs support GBM progression. We hypothesize that understanding context-dependent GBM-GAM symbiosis may reveal the molecular basis of GBM tumorigenesis and lead to novel candidate treatment approaches aiming to improve GBM patient outcomes.

Proton therapy reduces the likelihood of high-grade radiation-induced lymphopenia in glioblastoma patients: phase II randomized study of protons vs photons

BACKGROUND

We investigated differences in radiation-induced grade 3+ lymphopenia (G3+L), defined as an absolute lymphocyte count (ALC) nadir of <500 cells/µL, after proton therapy (PT) or X-ray (photon) therapy (XRT) for patients with glioblastoma (GBM).

METHODS

Patients enrolled in a randomized phase II trial received PT (n = 28) or XRT (n = 56) concomitantly with temozolomide. ALC was measured before, weekly during, and within 1 month after radiotherapy. Whole-brain mean dose (WBMD) and brain dose-volume indices were extracted from planned dose distributions. Univariate and multivariate logistic regression analyses were used to identify independent predictive variables. The resulting model was evaluated using receiver operating characteristic (ROC) curve analysis.

RESULTS

Rates of G3+L were lower in men (7/47 [15%]) versus women (19/37 [51%]) (P < 0.001), and for PT (4/28 [14%]) versus XRT (22/56 [39%]) (P = 0.024). G3+L was significantly associated with baseline ALC, WBMD, and brain volumes receiving 5‒40 Gy(relative biological effectiveness [RBE]) or higher (ie, V5 through V40). Stepwise multivariate logistic regression analysis identified being female (odds ratio [OR] 6.2, 95% confidence interval [CI]: 1.95‒22.4, P = 0.003), baseline ALC (OR 0.18, 95% CI: 0.05‒0.51, P = 0.003), and whole-brain V20 (OR 1.07, 95% CI: 1.03‒1.13, P = 0.002) as the strongest predictors. ROC analysis yielded an area under the curve of 0.86 (95% CI: 0.79-0.94) for the final G3+L prediction model.

CONCLUSIONS

Sex, baseline ALC, and whole-brain V20 were the strongest predictors of G3+L for patients with GBM treated with radiation and temozolomide. PT reduced brain volumes receiving low and intermediate doses and, consequently, reduced G3+L.

Immune biology of glioma-associated macrophages and microglia: functional and therapeutic implications

CNS immune defenses are marshaled and dominated by brain resident macrophages and microglia, which are the innate immune sentinels and frontline host immune barriers against various pathogenic insults. These myeloid lineage cells are the predominant immune population in gliomas and can constitute up to 30-50% of the total cellular composition. Parenchymal microglial cells and recruited monocyte-derived macrophages from the periphery exhibit disease-specific phenotypic characteristics with spatial and temporal distinctions and are heterogeneous subpopulations based on their molecular signatures. A preponderance of myeloid over lymphoid lineage cells during CNS inflammation, including gliomas, is a contrasting feature of brain immunity relative to peripheral immunity. Herein we discuss glioma-associated macrophage and microglia immune biology in the context of their identity, molecular drivers of recruitment, nomenclature and functional paradoxes, therapeutic reprogramming and polarization strategies, relevant challenges, and our perspectives on therapeutic modulation.

Mature myelin maintenance requires Qki to coactivate PPARβ-RXRα-mediated lipid metabolism

Lipid-rich myelin forms electrically insulating, axon-wrapping multilayers that are essential for neural function, and mature myelin is traditionally considered metabolically inert. Surprisingly, we discovered that mature myelin lipids undergo rapid turnover, and quaking (Qki) is a major regulator of myelin lipid homeostasis. Oligodendrocyte-specific Qki depletion, without affecting oligodendrocyte survival, resulted in rapid demyelination, within 1 week, and gradually neurological deficits in adult mice. Myelin lipids, especially the monounsaturated fatty acids and very-long-chain fatty acids, were dramatically reduced by Qki depletion, whereas the major myelin proteins remained intact, and the demyelinating phenotypes of Qki-depleted mice were alleviated by a high-fat diet. Mechanistically, Qki serves as a coactivator of the PPARβ-RXRα complex, which controls the transcription of lipid-metabolism genes, particularly those involved in fatty acid desaturation and elongation. Treatment of Qki-depleted mice with PPARβ/RXR agonists significantly alleviated neurological disability and extended survival durations. Furthermore, a subset of lesions from patients with primary progressive multiple sclerosis were characterized by preferential reductions in myelin lipid contents, activities of various lipid metabolism pathways, and expression level of QKI-5 in human oligodendrocytes. Together, our results demonstrate that continuous lipid synthesis is indispensable for mature myelin maintenance and highlight an underappreciated role of lipid metabolism in demyelinating diseases.

The Role and Therapeutic Targeting of JAK/STAT Signaling in Glioblastoma

Glioblastoma remains one of the deadliest and treatment-refractory human malignancies in large part due to its diffusely infiltrative nature, molecular heterogeneity, and capacity for immune escape. The Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling pathway contributes substantively to a wide variety of protumorigenic functions, including proliferation, anti-apoptosis, angiogenesis, stem cell maintenance, and immune suppression. We review the current state of knowledge regarding the biological role of JAK/STAT signaling in glioblastoma, therapeutic strategies, and future directions for the field.